The transmission of digital video data streams from a source such as a television camera or motion picture to a viewing display involves very high data rates. A number of data compression schemes have therefore been developed or proposed to reduce the actual transmission bit rate requirement while preserving high quality images. One such development has been adopted by the International Standards Organization (ISO) as standard ISO 11172-2 entitled "Coding of Motion Pictures and Associated Audio for Digital Storage Media at up to about 1.5 Mbit/sec." This standard is commonly referred to as "MPEG-1". A second standard also adopted by ISO is ISO 13818-2 entitled "Generic Coding of Moving Pictures and Associated Audio Information: Video," referred to as "MPEG-2".
In some applications it may be desirable to display the video data at the receiving end with a reduced size. For example, one may wish to watch one video on a television screen while monitoring a second video of lesser importance in a reduced size window within the larger television screen. Such techniques sometimes referred to as Picture in Picture (PIP) are well known in the analog television art. Arai in U.S. Pat. No. 5,083,205 for example describes a receiver with multiple demodulators to produce a PIP display format. Aimonoya in U.S. Pat. No. 5,047,858 describes a method of combining images from several analog sources on the screen of a single television monitor. Filliman, et al. in U.S. Pat. No. 5,486,871 describe a control system for an adjustable deflection system to expand or shrink the size of video images on a display screen.
In general these techniques require the use of multiple tuners or multiple demodulators, one for each video source one wishes to view, and then reducing the effective size of one or more of the analog images before combining the images for display. All of the video sources are displayed in real time. One can also combine images at the source site before transmission, and then send out a single analog video with the combined images, with at least one in a reduced size window. In this case an ordinary receiver with a single tuner and single demodulator can be used, however individual viewers would have no choice in the particular combination selected at the source site.
More recently, various techniques have been developed for scaling the size of a digital video image at the receiver. Lim, in U.S. Pat. No. 5,444,491 describes a television receiver for determining the transmission format (e.g. resolution and frame rate) of encoded image frames, and properly displaying the image on the viewer display, including scaling up or down to fit the display size. Willis in U.S. Pat. No. 5,365,278 describes digitizing analog video signals. The digitized signals are then modified in a signal processing circuit to represent pictures in sizes smaller than the video display.
Chaddha, in U.S. Pat. No. 5,742,892 describes a decoder for upscaling the size of a small video by upsampling to increase the number of pixels displayed. McNeil, et al. in U.S. Pat. No. 5,790,714 describes scaling down by using area weighted averages of pixels in both the vertical and horizontal directions. To scale up an interpolation or replication process is used to double the pixel grid which is then scaled down to a final size greater than the original pixel grid using the area weighted average process. Puri, et al. in U.S. Pat. No. 5,253,056 describe an adaptive technique for encoding, and subsequently decoding scalable video signals. Schafer, in U.S. Pat. No. 5,402,513 describes a decoder for generating a scaled video output.
Japanese patent JP 9083896 describes decoding and scaling video data from multiple channels which has been multiplexed together along with an address generation indication into a single source. The resulting display shows the multiple channels simultaneously, in reduced from.
Scaling is also used to convert movie videos which typically have a 9:16 aspect ratio; that is the ratio of this height to the width is 9 to 16; to a television display which in the U.S. is about 3:4. One method called "letterbox" involves appending a blank area to the top and bottom of each picture in a movie video so that the total aspect ratio of the original picture plus blank area is 3:4. Another method called "pan-scan" selects a 3:4 ratio subpicture from a 9:16 picture, discarding the rest. The location of the selected subpicture may vary from picture to picture i.e. the most important part may be chosen, so that the selected subpicture is moved from left to right in a camera pan fashion as needed. As described by Linzer in U.S. Pat. No. 5,638,130 these two scaling methods can be applied at either the transmission end, in which case the receiver doesn't have to do anything, or else the receiver can do the scaling conversion. Pan and Scan data can be multiplexed with the video signal before transmission as described by Masaru, et al. in JP 9093541A. If the receiver has a 3:4 display, then the pan-scan data is used to select the 3:4 ratio subpicture and discard the rest. In the case where the receiver has a 9:16 display, the entire video image is displayed.
While the foregoing methods permit several video sources to be displayed on a single display screen with some or all in reduced size, this is accomplished by duplicating most of the decoding and scaling apparatus and only at the end combining the sources onto one screen image. In many applications this duplication is unnecessary and wasteful. For example, a program guide comprising a still image of each channel is usually sufficient, particularly if the still image is a relatively recent e.g. within the past few minutes, frame from the program in progress on that channel. In some security surveillance applications, a still image taken every few minutes may suffice. The viewer could then make a selection of which video source to watch in real time based on the still images. The source of video data could be television cameras located at various positions about a surveillance site. More remote sources could also be included by sending data over a cable, data network, or the internet.
Accordingly with the teachings of the present invention, there is provided a system for displaying multiple sources in a reduced size on a single display without use of expensive equipment duplication at the viewing location.
It is believed that such a system constitutes a significant advancement in the art.